1. Field of the Invention
The present invention relates to certain novel UV light absorbing monomers and polymers and lenses prepared therefrom.
2. Prior Art
There exists the need for the provision of polymeric materials which are not degraded by or otherwise affected by ultraviolet light. Polymeric materials such as implants, lenses, etc., presently suffer from the disadvantage of ultraviolet light-induced degradation. Currently employed polymeric materials for the manufacture of ocular lenses, etc., incorporate stabilizers which absorb a large quantity of the ultraviolet light or quench the energy which results from excitation of groups in the polymeric material as a result of ultraviolet radiation. The extractability of these stabilizers, however, detract from their usefulness since they are subject to extraction by body fluids or other liquids thereby raising the problems of contamination, toxicity, etc.
It is also necessary, in some instances, to provide lenses manufactured from materials which absorb ultraviolet light thereby overcoming a condition in the eye which prevents the ordinary absorption of ultraviolet light. For example, the aphakic eye contains no crystalline lens which ordinarily absorbs light at wavelengths from about 300 up to about 400 nm. Since the entire spectrum of light striking the retina in the aphakic eye is significantly different from that in the normal eye, corrective means are necessary to restrict the spectrum striking the retina therein.
Copolymerizable monomers containing functional groups capable of absorbing ultraviolet light have been synthesized. The copolymerization of such monomers with those ordinarily employed to manufacture lenses and ocular implants, etc., result in the formation of materials resistant to degradation upon exposure to ultraviolet light with decreased extractability and volatility. See, for example, U.S. Pat. Nos. 4,304,895; 4,310,650; 3,162,676; 4,390,676 and 4,528,311.
The monomers and systems described by the above-listed patents use relatively inefficient benzophenone or benzotriazole UV absorbing vinyl monomers and therefore require the inclusion of relatively large amounts of the UV absorbing monomer in the copolymer. For UV absorbing intraocular lenses with optics capable of absorbing 95% of the light below 400 nm (5% transmission), for example, concentrations of 5-10 wt % of benzophenone and 1-5% or more of benzotriazole monomers are required. The use of such high UV absorbing comonomer concentrations is accompanied by significant inefficiency in copolymerization with methylmethacrylate, for example, due to the radical inhibitor properties of the UV absorber; thereby resulting in substantially reduced monomer conversions, low molecular weight polymers, and large amounts of UV absorber unreacted monomers which can act as biotoxic impurities.
Accordingly, it is an object of the present invention to provide novel ultraviolet light absorbing monomers which are more efficient UV absorbers and are capable of copolymerization with monomers in relatively small amounts to prepare ocular materials capable of absorbing ultraviolet light.
The provision of such a monomer enables the preparation of ocular materials having a extremely low concentration of the ultraviolet absorber thereby ensuring optimum long-term implant biocompatibility and usefulness of the lens.